Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-05-08
2002-01-01
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S110000, C349S138000
Reexamination Certificate
active
06335772
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display device and its manufacturing method especially suitable for application to a liquid crystal display having an electrically-conductive light-shading layer provided in a level above a thin film transistor for driving pixel electrodes and below the pixel electrodes.
2. Description of the Related Art
Liquid crystal display devices are widely used as flat-type displays. As a thin film transistor (TFT) for driving pixel electrodes in such a liquid crystal display, amorphous silicon (a-Si) TFT was used conventionally. Recently, however, polycrystalline SiTFT has come to be used often.
Photosensitivity of polycrystalline SiTFT is not so high as that of a-SiTFT. Recently, however, liquid crystal display devices such as projector have increasingly been used under intensive light, and light leak current is no more negligible even with polycrystalline SiTFT. As a result, degradation of contrast and deterioration of the image quality such as cross-talk and flicker, for example, have arisen as problems.
In liquid crystal display devices, light from light source is usually introduced from the side of the opposed substrate. As to prevention of light from entering into polycrystalline SiTFT, as disclosed in Japanese Patent Laid-Open Publication No. hei 5-100250 and Japanese Patent Application No. hei 10-307465, for example, by locating the electrically-conductive light-shading layer (black matrix) conventionally provided on the opposed substrate to the level above the polycrystalline SiTFT of a TFT substrate, which is nearer to the polycrystalline SiTFT, reduction of such light has been attained.
However, according to the knowledge of the inventor, in the techniques disclosed in the documents, Japanese Patent Laid-Open Publication No. hei 5-100250 and Japanese Patent Application No. hei 10-307465, due to the phenomenon that the thickness of the electrically-conductive light-shading layer becomes thinner in level-difference portions caused by unevenness of the underlying insulating layer, in other words, the phenomenon that the step coverage degrades, the shading performance is insufficient at the level-difference portions. Therefore, under high-luminance irradiation of light, leak light from level-difference portions causes generation of a light leak current, and deterioration of the image quality cannot be prevent under the current technologies.
This problem is discussed below in greater detail.
FIG. 1
shows a TFT substrate of a conventional active matrix type liquid crystal display device. As shown in
FIG. 1
, a shading layer
102
is provided on a shading region of a quartz glass substrate
101
, and an inter-layer insulating film
103
is provided to cover the shading layer
102
. Formed on the inter-layer insulating film
103
is a polycrystalline Si film
104
of a predetermined pattern, and a gate insulating film
105
is provided to cover the polycrystalline Si film
104
. A gate wiring
106
is formed on the gate insulating film
105
. Although not shown, the polycrystalline Si film
104
has formed therein a source region and a drain region (not shown) in self alignment with the gate wiring
106
. The gate electrode made of the gate wiring
106
and those source region and drain region make up a polycrystalline SiTFT for driving pixel electrodes. On a predetermined portion of the gate insulating film
105
above the drain region, an electrode
107
is provided. This structure interposing the gate insulating film
105
between this electrode
107
and the drain region constitutes a holding capacitor element.
An inter-layer insulating film
108
is provided to cover the gate wiring
106
and the electrode
107
. Contact holes
109
and
110
are formed at predetermined portions of the inter-layer insulating film
108
and the gate insulating film
105
. In the shading region, a lead-out electrode
111
is provided in connection with the drain region of the polycrystalline SiTFT through the contact hole
109
, and a signal wiring
112
is provided in connection with the source region of the polycrystalline SITFT through the contact hole
110
. An inter-layer insulating film
113
is formed to cover these lead-out electrode
111
and the signal wiring
112
. In a predetermined location on the inter-layer insulating film
113
, a SiN film
114
made by plasma CVD lies. The SiN film
114
mainly inactivates dangling bonds in the polycrystalline Si film
104
with hydrogen, and functions as a hydrogen supply source for improving the property of the polycrystalline SiTFT. Further provided is a contact hole
115
in a predetermined portion of the inter-layer insulating film
113
above the lead-out electrode
111
. In contact with the lead-out electrode
111
through the contact hole
114
, an electrically-conductive light-shading layer
116
is provided on the inter-layer insulating film
113
, and an electrically-conductive light-shading layer
117
is provided on the SiN film
114
. The structure stacking these electrically-conductive light-shading layer
116
,
117
, lead-out electrode
111
and signal wiring
112
shields the incident light from above over the entire region other than the pixel aperture region. An inter-layer insulating film
118
is provided to cover the electrically-conductive light-shading layers
116
,
117
. The inter-layer insulating film
118
has formed a contact hole
119
in a predetermined location above the electrically-conductive light-shading layer
116
. On the inter-layer insulating film
118
, a transparent pixel electrode
120
is provided in connection with the electrically-conductive light shading layer
116
through the contact hole
119
. An orientation film
121
of a liquid crystal (not shown) is provided to cover the pixel electrode
120
.
In the conventional liquid crystal display apparatus explained above with reference to
FIG. 1
, since the electrically-conductive light-shading layers
116
,
117
are formed on the inter-layer insulating film
113
which includes a large unevenness reflecting the stepped configuration of the base layer, step coverage of these electrically-conductive light-shading layers
116
,
117
degrades. Therefore, the light shading performance of these electrically-conductive light-shading layers
116
,
117
was not sufficient in these step portions, which invited generation of a light leak current by leak light from level-difference portions under high-luminance irradiation of light, and deterioration of the image quality could not be prevented.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a liquid crystal display device and its manufacturing method which can improve the light shading performance of an electrically-conductive light shading layer and can prevent deterioration of the image quality caused by a light leak current.
According to the invention, there is provided a liquid crystal display device having a thin-film transistor for driving a pixel electrode on a substrate and an electrically-conductive light-shading layer lying in a level above the thin film transistor and below the pixel electrode, comprising:
the electrically-conductive light-shading layer being formed on a smoothed layer.
There is further provided a liquid crystal display device having a first light-shading layer formed on a substrate, a thin film transistor for driving a pixel electrode formed on the first light shading layer, and a second light-shading layer formed in a level above the thin-film transistor and below the pixel electrode, comprising:
the second light-shading layer being formed on a smoothed layer.
There is further provided a method for manufacturing a liquid crystal display device having a thin-film transistor for driving a pixel electrode on a substrate and an electrically-conductive light-shading layer lying in a level above the thin film transistor and below the pixel electrode, characterized in:
the electrically-conductive light-shading layer being formed on a smoothed l
Abe Fumiaki
Hashimoto Makoto
Sato Takusei
Chowdhury Tarifur R.
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
Sikes William L.
Sony Corporation
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